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  1. This chapter focuses on general concepts of protein function to lay groundwork for all of the metabolism pathways coming up

  2. There are some topics important for Step 1 that we focus on here

    1. Enzyme kinetics

    2. Muscle contraction

    3. Diseases: Marfan's syndrome, cystic fibrosis

  3. Try to group proteins into the ones that do something (i.e., enzymes) and the ones that don't do much (e.g., structural proteins)

  4. Learning about basics of protein function and nomenclature can help you make educated guesses on difficult questions

Structural Proteins

  1. Some important diseases arise from defects in structural proteins, as opposed to proteins that carry out more active functions


  1. Intracellular structure and cell motility

  2. Microtubules (MTs): In cytosol and cilia — movement of specific things inside the cell

    1. Tubulin heterodimers form the basic structure

    2. Kinesin and dynein are motor proteins that “walk” along MTs

  3. Actin: Cell structure (microfilaments), microvilli, and scaffold for myosin

    1. Actin fibrils are the major structural component of muscles and enable contraction

  4. Intermediate filaments: Varied, used in histopathology to identify cell types

  5. Antimicrobial and anticancer drugs target MTs as “active” in these cell types

    1. Vincristine and vinblastine inhibit MT formation to prevent mitosis of cancer cells

    2. Paclitaxel “locks” MTs in mitosis so cancer cells can't complete division

    3. Colchicine affects neutrophil motility (important for gout)

    4. Mebendazole and griseofulvin affect MT formation in parasites and fungi

  6. Microtubule defects lead to developmental disorders

    1. Kartagener syndrome: Cilia are dysfunctional because of MT motor protein → developmental, reproductive, respiratory problems

Table 4-1.Intermediate filament stains (review).
Figure 4-1.

Cytoskeletal proteins.

Figure 4-2.

Anti-microtubule drugs.


  1. Extracellular space: Provides scaffold to support connective tissue and skin

  2. Collagen is a key component (reviewed in Chapter 3)

  3. Elastin: Springy substance in organs that need to stretch

    1. Like collagen, has glycine, proline, lysine

    2. Also like collagen, crosslinking of fibers requires lysyl oxidase

      • Inhibition of lysyl oxidase can cause aortic weakness (mimicking Marfan's syndrome)

    3. Differs from collagen on a biochemical level: No hydroxylation

  4. Fibrillin: Another elastic protein that complexes with elastin to provide stretch

  5. α1-antitrypsin deficiency is due to excessive breakdown of elastin because of overactive elastase → emphysema

    1. Lungs primarily affected: Panacinar emphysema

    2. Liver also affected: Site of α1-antitrypsin synthesis

      • Liver is damaged due to accumulation of misfolded protein

  6. Marfan's ...

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